One-piece can bodies, meaning can bodies in which the cylindrical side wall is formed integrally with the bottom wall, are normally formed by a drawing and ironing operation. To provide increased strength for the bottom wall to resist the internal pressure of the contained liquid, certain can bodies, in the past, have been formed with a radius along the peripheral edge of the bottom wall and a central inwardly extending dome or concavity.
More recently, one-piece can bodies have been formed with an inwardly beveled edge along the periphery of the bottom wall which borders a central dome or concavity of smaller diameter. This configuration increases the strength of the bottom wall, enabling the bottom wall to be formed of lesser gauge metal and results in a substantial cost saving. However, in forming the central dome, there is a tendency for the beveled peripheral edge to be wrinkled or deformed which can adversely effect the strength characteristics of the bottom wall. Consequently, doming dies have included a pressure ring which is adapted to engage the beveled edge as the dome is being formed, and in conjunction with a punch on the inside of the can body, aid in preventing the beveled edge from being deformed. In the conventional doming mechanism, the pressure ring is connected to a plurality of air bags which are located outwardly of the die assembly. The air bags provide a substantially uniform reactive force against the beveled edge as the dome is being formed, to thereby prevent wrinkling or other deformation in the beveled edge.